style.css

/* Author: Salvador Guerrero */

* {
    box-sizing: border-box;
}

body {
    background-color: black;
    margin: 0;
}

textarea {
    font-size: 1em;
    color: lawngreen;
    resize: none;
    width: 100%;
    height: 100%;
    border: 1px solid darkgreen;
    background-color: #1e1e1e;
}

button {
    height: 100%;
    width: 20%;
    cursor: pointer;
    font-size: 1em;
    border: 0;
    background-color: #1e1e1e;
}

button:hover {
    background-color: #282828;
}

button:focus {
    outline:0;
}

.textStyle {
    color: #68db00;
    font-family: "Andale Mono",monospace;
}

.largeTextDiv {
    width: 100%;
    display:inline-block;
    height: 50%;
}

.verticalLine {
    border-left: 1px solid darkgreen;
    height: 100%;
}

#container {
    margin: auto;
    width: 80%;
    height: 80vh;
}

#inputDiv {
    padding-top: 1.4em;
    padding-bottom: 2em;
    border: 0;
}

#resultDiv {
    padding-top: -2em;
    padding-bottom: 3em;
    border: 0;
    pointer-events: none;
}

#buttonsDiv {
    height: 4em;
    margin: -2em 0 0 0;
    width: 100%;
    display: flex;
    /* didn't work: flex-direction: column;*/
    align-items: center;
    border-top: 0;
    border-right: 1px solid darkgreen;
    border-bottom: 0;
    border-left: 1px solid darkgreen;
}

.verticalStack {
    height: 100%;
    width: 20%;
    /*display: flex;*/
    /*align-items: center;*/
    /*height: 50px;*/
    /*border: 1px solid red;*/
}

.smallLabel {
    display: inline-block;
    box-sizing: border-box;
    height: 50%;
    line-height: 200%;
    padding-left: 0.25em;
}

.smallInput {
    display: inline-block;
    box-sizing: border-box;
    width: 100%;
    height: 50%;
    padding-left: 0.5em;
    border: 1px solid #ccc;
}

#header {
    font-size: 1em;
    display:inline-block;
    width: 100%;
    margin: 0 0 -1.4em 0;
    padding: 0.2em 0 0 0.2em;
    border: 0;
}

#footer {
    font-size: 0.5em;
    display:inline-block;
    width: 100%;
    margin: -5.8em 0 0 0;
    padding: 0.2em 0 0 0.2em;
    border: 0;
    vertical-align: center;
}

/* Responsive layout - when the screen is less
 * than 600px wide, make the two columns stack
 * on top of each other instead of next to each
 * other */
@media screen and (max-width: 600px) {
    #container {
        width: 95%;
    }
}

@media screen and (max-height: 600px) {
    #container {
        height: 95vh;
    }
}