style.css

@import url('https://fonts.googleapis.com/css?family=Roboto:100,400,700');

/**
 *  Body & Page layout
 */

body {
    font-family: 'Roboto', sans-serif;
    text-transform: uppercase;
    display: flex;
    margin: 0;
    height: 100vh;
}

header {
    position: relative;
    background-color: #34495e;
	  z-index: 1;
}

main {
    position: relative;
    background-color: #ecf0f1;
}

header, main {
  height: 100vh;
  flex-shrink: 0;
}

@media screen and (max-width: 890px) {
    header {
        height: 150px;
        padding-top: 1.4em;
    }
    body { flex-direction: column; }
}

@media screen and (min-width: 891px) {
    /* header, main { float: left; } */
    body { flex-direction: row; }

    header { width: 22vw; }

    main { width: 78vw; }

    #hgroup {
        position: absolute;
        top: 50%;
        margin-top: -67.8px;
    }
}

/**
 * Header
 */

h1, h3 {
    color: white;
    margin: 0;
}

h1 {
    font-weight: 700;
    margin-bottom: 0.4em;
}

h3 {
    font-weight: 200;
    font-size: 0.9em;
}

#hgroup {
    width: 100%;
    text-align: center;
}

#newGameButton {
    position: absolute;
    bottom: 0;
    width: 100%;
    background-color: white;
    border: none;
    padding: 17px;
	margin: 0;
    font-size: 0.8em;
    font-weight: 700;
    cursor: pointer;
	text-transform: uppercase;
	
	transition: all 200ms ease-in-out;
	-webkit-transition: all 200ms ease-in-out;
	-moz-transition: all 200ms ease-in-out;
	-o-transition: all 200ms ease-in-out;
}

#newGameButton:focus { outline: none; }

#newGameButton:hover { background-color: #ddd; }

/**
 * Main: Tic Tac Toe
 */

#tictactoe {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;

    height: 85vmin;
    width: 85vmin;
    margin: auto;
}

@media screen and (max-width: 890px) {
    #tictactoe {
        height: 70vmin;
        width: 70vmin;
    }
}

.square {
    width: calc(33.33% - 6px);
    height: calc(33.33% - 6px);
    float: left;
    cursor: pointer;
}

/** Central column **/
.square[data-col="1"] {
    border-left: 6px #abb7b7 solid;
    border-right: 6px #abb7b7 solid;
}

/** Central row **/
.square[data-row="1"] {
    border-top: 6px #abb7b7 solid;
    border-bottom: 6px #abb7b7 solid;
}

.square:not(:empty) { cursor: auto; }

/* SVG */

#tictactoe svg { margin: 3px; }

svg path {
    fill: none;
    stroke-width: 8px;
	
	-webkit-animation: svg_draw 0.225s cubic-bezier(0.4, 0, 0.2, 1) forwards;
	animation: svg_draw 0.225s cubic-bezier(0.4, 0, 0.2, 1) forwards;
}

svg path:last-of-type {
	-webkit-animation-delay: 0.125s;
	animation-delay: 0.125s;
}

svg.circle path {
	stroke: #3498db;
    stroke-dasharray: 301.635;
	stroke-dashoffset: 301.635;
}

svg.cross path {
	stroke: #fdd835;
    stroke-dasharray: 135.764;
	stroke-dashoffset: 135.764;
}

/* SVG Animation */

@keyframes svg_draw {
  to { stroke-dashoffset: 0; }
}

/**
 * Modal
 */

#modal {
	opacity: 0;
	pointer-events: none;
	
	z-index: 1;
	overflow: hidden;
	
	position: absolute;
	top: 0;
	left: 0;
	right: 0;
	bottom: 0;
	
	transition: all 200ms ease-in-out;
	-webkit-transition: all 200ms ease-in-out;
	-moz-transition: all 200ms ease-in-out;
	-o-transition: all 200ms ease-in-out;
}

#modal.visible {
	opacity: 1;
	pointer-events: auto;
}

/* Background (blur o blackish) */
@supports (-webkit-backdrop-filter: blur(10px)) or (backdrop-filter: blur(10px)) {
	#modal {
    	-webkit-backdrop-filter: blur(10px);
		backdrop-filter: blur(10px);
	}
}

@supports not ((-webkit-backdrop-filter: blur(10px)) or (backdrop-filter: blur(10px))) {
	#modal { background-color: rgba(0,0,0,0.6); }
}

#modal-content {
	position: absolute;
    top: calc(50% - 100px);
    left: calc(50% - 200px);
    width: 400px;
    background-color: rgba(255,255,255,0.9);
	
	box-shadow: 0 14px 28px rgba(0,0,0,0.25), 0 10px 10px rgba(0,0,0,0.22);
}

#modal-content h2 {
	font-weight: 400;
    text-align: center;
}

#result-symbol {
	text-align: center;
    margin: 0.83em auto;
}

#result-symbol > svg { height: 120px; }